The nucleus paragigantocellularis lateralis (PGCL) has been described as being the chemosensitive area of the brain stem. It is known that PGCL modifies cardiovascular activity and respiration. Preganglionic sympathetic neurons and the parabrachial nucleus are two target areas of PGCL efferents. Other projections of the PGCL are still unknown. The experiments described in this proposal will document the total projection of PGCL neurons and determine if other brain stem nuclei which control respiration and cardiovascular activity receive PGCL efferents. It is important to know if nuclei which modify autonomic activity are controlled by the same sets of neurons. Compounds which fluoresce at different wavelengths (and hence colors) will be injected into two synaptic targets of PGCL, one chemical will be injected into one site only. The nuclei injected will be those known to influence autonomic activity. The injected compounds will flow retrogradely down the axon to the cell body. It will then be ascertained if a single neuron projects to more than one area which controls autonomic activity. Electron microscopic studies will document the fine structure of PGCL and determine the anatomical substrate of chemosensation in PGCL. The synaptology of PGCL also will be determined. The PGCL also is a potent site for producing naloxone-reversible analgesia and is the origin of some reticulospinal neurons which contain met-enkephalin. Immunohistochemistry of enkephalins, substance-P and serotonin will be done at the light and electron microscopic levels. Results of these experiments will be correlated with our knowledge of the cytology and connections of the PGCL. Immunochemical studies of these putative neurotransmitters will allow us to document morphological connections between these systems. Thus, we will bridge the gap between structural and functional studies and learn how chemosensation and analgesia are effected through these chemical systems.